In recent years, with the gradual development of the advanced equipment manufacturing industry toward the trend of precision and ultra-precision, especially the constant improvement of the performance of the aircraft engine, the precision of engine processing and assembly is required to be higher and higher. Particularly, in the pursuit of high thrust-weight ratio, the impact of factors, such as engine vibration and noise generated due to assembly errors, on the performance becomes gradually prominent, which poses severe challenge for the performance of the testing equipment of the engine, and also has higher requirement on the performance of the workbench used for adjustment and positioning. For processing and assembly of the engine, the workbench is not only required to have a function of two-dimensional adjustment in a plane, but also required to adjust the tilt angle of the workpiece and realize the function of inclination adjustment.
Engine vibration is an important factor affecting the safety of an aircraft, and is also an important indicator reflecting the engine performance. Engine turbine component, having a high rotation speed and large weight, is a major source of engine vibration. To reduce such impact, in addition to eliminating it in the testing process of dynamic balance of the engine, the assembly process should also be strictly controlled, because engine assembly is a step previous to the dynamic balancing, and vibration due to unsuitable assembly will be enlarged by 100 to 1000 times at high-speed rotation and suitable assembly can largely reduce the pressure of dynamic balance. Therefore, as a key technique for improving the performance of the aircraft engine, the aircraft engine assembly testing technique has attracted more and more attention and become a hot research topic.
An aircraft engine is composed of turbine stator and rotor which are in complex structures. The stator and rotor are required to have high concentricity themselves, and also need to be highly concentric after assembly. The high-pressure turbine rotor has a cantilever structure, so a slight imbalance and disturbance will cause a large vibration response. At present, there are many studies on the elimination of vibration of the aircraft. Many measures, such as eliminating the axial and radial deflection of the turbine stator and rotor, ensuring the concentricity of the bearing support of the turbine, and guaranteeing the consistency between the final assembly and the assembly before dynamic balancing, etc., can solve the problem of engine vibration well, and these measures can he controlled in the process of assembling the engine.
The objects of the test on the aircraft engine assembly are turbine stator and rotor. In the condition that the processing precision of the components meets the requirements, the final test is controlled by guaranteeing the assembly precision and concentricity, Rotation of the engine will generate high pressure, and the stator and rotor of the engine are composed of a plurality of single components which are stacked together. It is most desirable that the rotary axis of each component coincides with the axis of the entire engine. In operation, the large-scale engine has a high-speed rotation speed of greater than 10000 rpm, so the axial or radial deflection of the single component will inevitably result in deviation of the center of the turbine disk from the rotation axis of the engine. A very large centrifugal force will be produced under such condition, which will lead to unbalance of the rotor rotation and engine vibration, thereby ensuring the concentricity of each component is the important and difficult issue to be solved during mounting.
A British company, TAYLOR HOBSON LTD., has developed a three-point centering and leveling workbench, whose table surface is supported by three supporting points A, B, P which can form an equilateral triangle, wherein point P is fixed, and the other two points A and B are arranged with driving mechanisms and are vertically slightly movable, so as to adjust the tilt angle of the workpiece (A. B. Bamaby, M. W. Mills, H. R. Lane, Metrological apparatus workpiece position controller-automatically centres and levels by computer using surface data from transducer with transverse compensation after tilting. EP240150-A2.1987:2˜8). The workbench directly bears the loads with a driving mechanism, and all the weight of the load rests on the three supporting points, which requires the driving mechanism to have great driving force. Yet, such workbench cannot be used in case of large load.
Japan Tokyo Seimitsu Company designed a worktable which could perform centering and leveling adjustments in two perpendicular directions, respectively, and provided a method of obtaining the leveling adjustment in the direction of the axis of a workpiece by using a plurality of measurement cross-sections (Katamachi, Shouzou. Roundness Measurement Apparatus. US2008015 4540. 2008:1˜5).
Patent No. CN201110450087, “a large three-dimensional adjustment platform for a multifunctional measuring instrument”, presented a large three-dimensional adjustment platform for a multifunctional measuring instrument; two telescoping motors distributed in the platform can push the middle platform to rotate around the rotation assembly, and drive the upper platform to rotate as well, so as to realize adjustment to the inclined deflection of the workpiece in Z direction. However, the inclination adjustment of the platform can only be performed by rotating around one rotation assembly, so the inclination adjustment is limited in ability and low in precision.
Patent No. CN98229568.5, “High precision, fast and automatic leveling mechanism”, proposed a high precision and fast leveling mechanism, whose working principle is as follows: the motor drives the eccentric cam to rotate, the spring in the base causes the thimble and the eccentric cam to be pressed against each other, driving the positioning nails and calibration plate to move up and down along the bearing sleeve; the calibration plate is an air-floating thrust bearing with a number of throttling pores uniformly distributed on the end surface; a component-bearing platform is connected to the hemisphere, and when compressed air is introduced between the hemisphere and the hemisphere seat, the component-bearing platform can rotate around the spheric center of the hemisphere seat, and is driven by the rising cylinder to move up and down. When the workpiece approaches the calibration plate, a gas film is formed to make the workpiece indirectly abut with the plate and level the workpiece.
A common problem of the prior arts described above is that high precision and high displacement sensitivity of the adjustment apparatus cannot be guaranteed in case of large load. However, in the assembly of the aircraft engine, the rotatory assemblies such as leaf blades are hundreds of kilograms, and the blades are assembled directly on the workbench, which requires the adjustment workbench capable of bearing large loads and having high adjusting and positioning precision.